Add defaults_visibility support

Bug: 130796911
Test: m nothing
Change-Id: I7b9462d3360be2bbeaf6ff38c5328f45ff5b5ebb
diff --git a/android/module.go b/android/module.go
index 5bb1177..138b9cd 100644
--- a/android/module.go
+++ b/android/module.go
@@ -305,6 +305,11 @@
 	// If no `default_visibility` property can be found then the module uses the
 	// global default of `//visibility:legacy_public`.
 	//
+	// The `visibility` property has no effect on a defaults module although it does
+	// apply to any non-defaults module that uses it. To set the visibility of a
+	// defaults module, use the `defaults_visibility` property on the defaults module;
+	// not to be confused with the `default_visibility` property on the package module.
+	//
 	// See https://android.googlesource.com/platform/build/soong/+/master/README.md#visibility for
 	// more details.
 	Visibility []string